Method And Arrangement For Operating A Steam Turbine Plant In Combination With Thermal Water Treatment

ABSTRACT

A system and method are provided for operating a steam turbine plant in combination with a thermal water treatment plant having a first condenser for condensing raw water from exhaust gas of a steam turbine, an evaporator for operation with raw water and air, wherein transfers of material and heat occur in the evaporator, a tank for receiving the raw water with increased concentrations of impurities, a second condenser for condensing the pure water from the air downstream of the evaporator, and at least one steam turbine for operation with the purified water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2015/060321 filed May 11, 2015, which designates the United States of America, and claims priority to DE Application No. 10 2014 217 280.2 filed Aug. 29, 2014, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a method and an arrangement for operating a steam turbine plant in combination with a thermal water treatment plant for purifying condensate from the exhaust gas of a steam turbine process.

BACKGROUND

Steam power plants are the predominant type of power plants for electricity generation. High demands are made of the water quality of the boiler feed water of the water circuit of such power plants. When the boiler feed water is vaporized to steam, depending on the design, liquid water is completely converted to the gas phase on hot surfaces. All non-volatile boiler feed water components are in this case deposited on this hot surface. As a disadvantage, said deposits hinder the heat transfer or lead to the mechanical failure of, for example, valves. In addition, many inorganic components in the boiler feed water cause the corrosion tendency of the component in the steam circuit to further increase. This can lead to stress cracks in components, in particular components made of steel.

To reduce the corrosive properties of water and/or steam in steam circuits, various methods of conditioning exist. These include, primarily, alkalization of the water and oxygen metering. Both an elevated pH and a reduced redox potential lead to a decreased solubility of iron oxide. However, alkalization using solid alkalization agents, disadvantageously, cannot be employed in continuous-flow heaters, since, here, the water is completely vaporized and thus deposits would occur. Therefore, in this case, ammonia is frequently used as volatile alkalizing agent.

To free the boiler feed water of impurities, various treatment methods are known. These methods are generally based on ion exchange. However, ion exchange processes can also behave as sources of contamination. Breakdown products of the resin material can disadvantageously settle on dry surfaces of various components in the heating steam circuit. In addition, the boiler feed water can be cleaned up using a reverse osmosis process. However, in the reverse osmosis, high loadings of the raw water disadvantageously lead to a reduced flux in the reverse osmosis. In addition, the known methods are highly energy-intensive.

SUMMARY

One embodiment provides a method for operating a steam turbine plant in combination with a thermal water treatment plant having the following steps: condensing steam from the stream turbine plant to raw water in a first condenser, adding a carrier gas and at least one fraction of the raw water to an evaporator, wherein mass transfer and heat exchange take place in the evaporator between the raw water and the carrier gas, conducting the raw water and the carrier gas in counter flow in the evaporator, wherein the carrier gas heats up in the evaporator and takes up pure water from the raw water and the raw water cools and the contaminants concentrate, collecting the raw water with the concentrated contaminants downstream of the evaporator in a tank, conducting the carrier gas loaded with pure water into a second condenser, condensing purified water from the carrier gas in the second condenser, wherein the second condenser is cooled by the raw water from the tank, conducting the purified water into a steam circuit of the steam turbine plant, conducting the preheated raw water from the second condenser to a first heater, wherein heat from the steam turbine plant or the steam circuit transfers to the preheated raw water, and conducting the preheated raw water from the heater into the evaporator.

In one embodiment, the raw water comprises ammonia and the pH of the raw water is adjusted to be acidic in such a manner that the ammonia in the evaporator remains in the raw water.

In one embodiment, the raw water comprises ammonia and the pH of the raw water is adjusted to the basic in such a manner that the ammonia transfers into the carrier gas.

In one embodiment, fresh raw water is added to the tank.

In one embodiment, the fresh raw water is condensate water from the exhaust gas of the steam turbine, river water, seawater or wastewater.

In one embodiment, the temperature of the raw water in the evaporator is in the range 60° C. to 100° C.

In one embodiment, the heater is operated with the heat of the exhaust gas of a steam generator of the steam circuit.

In one embodiment, air is used as carrier gas.

Another embodiment provides an arrangement for operating a steam turbine plant in combination with a thermal water treatment plant having a first condenser for condensing steam from the steam turbine plant to raw water, an evaporator for operation with raw water and a carrier gas, wherein mass transport and heat exchange take place in the evaporator, a tank for collecting the raw water that is concentrated with contaminants, a second condenser for condensing the pure water from the carrier gas downstream of the evaporator, and at least one steam turbine for operation with at least a fraction of the purified water.

In one embodiment, the evaporator is a falling-film evaporator or a trickle-flow evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described hereinafter on the basis of an exemplary embodiment with reference to the attached drawings. In the drawings:

FIG. 1 shows an example arrangement having a steam circuit, turbine, condensers and thermal water treatment, according to one embodiment of the invention; and

FIG. 2 shows an example thermal water treatment arrangement having an evaporator and condenser, according to one embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide a method and an arrangement for treatment of water for a steam circuit, which overcome said disadvantages.

Some embodiments provide a method for operating a steam turbine plant in combination with a thermal water treatment plant. First, steam from a steam turbine plant is condensed in a first condenser to raw water. At least one fraction of the raw water is added with a carrier gas in an evaporator, wherein mass transfer and heat exchange take place in the evaporator between raw water and the carrier gas. The raw water and the carrier gas are conducted in counter flow in the evaporator. In this case, the carrier gas heats up in the evaporator and pure water is taken up from the raw water by the carrier gas. The raw water cools and the impurities, in particular the non-volatile impurities, concentrate in the raw water. The raw water with the concentrated impurities is collected in a tank downstream of the evaporator. The carrier gas loaded with pure water is conducted into a second condenser. In the second condenser, the purified water is condensed from the carrier gas, wherein the second condenser is cooled with raw water from the tank. The purified water is then recirculated to a steam circuit. The raw water that is preheated in the second condenser is conducted to a first heater, wherein heat transfers from the steam turbine plant or the steam circuit to the preheated raw water. The preheated raw water is thereafter conducted from the heater into the evaporator.

The arrangement for operation of a steam turbine plant in combination with a thermal water treatment plant may comprise a first condenser for condensing steam from the steam turbine plant to form raw water. In addition, it comprises an evaporator for operation with raw water and a carrier gas, wherein mass transport and heat exchange take place in the evaporator. In addition, the arrangement comprises a tank for collecting the raw water that is concentrated with contaminants. The arrangement further comprises a second condenser for condensing the pure water from the carrier gas downstream of the evaporator. The arrangement also comprises at least one steam turbine for operation with at least a fraction of the purified water.

The disclosed method and arrangement may utilize not only heat from the steam turbine process and the steam circuit, in particular the steam generator, but also components of the exhaust gas of the steam turbine, in particular the steam. The evaporation of the raw water from the exhaust gas of the steam turbine operates by the principle of forced convection. The second condenser cooled by raw water advantageously ensures the recovery of the heat of evaporation. The water and the carrier gas are advantageously conducted in counter flow through the evaporator. The temperature of the carrier gas increases in this case during the counter flow process, whereas the temperature of the raw water falls. At a height or separation stage of the evaporator, the air temperature is lower than the temperature of the raw water. Advantageously, by coupling the heat streams a low electrical energy demand and low miscellaneous operating costs of the cleanup process of the boiler feed water of the steam turbine are achieved. In addition, it is possible using the method, regardless of the quality of the raw water, to obtain as product completely demineralized water that was cleaned up of non-volatile components, with constant product quality. Advantageously, heat need only be provided at a low temperature level. The water treatment succeeds virtually without additional electrical energy input. The required thermal energy is advantageously taken off from the steam turbine plant or the steam circuit. The steam circuit typically comprises at least one steam generator, a plurality of condensers and heater.

In one embodiment, the raw water comprises ammonia as conditioning agent for the boiler feed water for the steam turbine process. In addition, the pH of the raw water is adjusted to be acidic upstream of the evaporator in such a manner that the ammonia in the evaporator remains in the raw water. Ammonia itself is a highly volatile component. Ammonia in water can be conditioned in such a manner that the ammonia is present as ammonium ion. This is the case for low pHs of at least one pH unit below the pKa value of ammonia of 9.2. If ammonia is present in water hydrolyzed as ammonium ion, it loses its volatility. As a result, it can be separated off in the evaporator since it is not converted into the gas phase.

It is likewise conceivable that ammonia is to be present in the water even after the cleanup, in order to affect the corrosion properties of the water. In this embodiment, the pH is selected to be high such that it is above the pKa of ammonia, such that it is highly volatile and co-transfers to the carrier gas and thus, together with the cleaned up water, can be recovered in the condenser. In this case, previously conditioned water is available as boiler feed water.

In an embodiment of the invention, fresh raw water is to be added to the tank. Said raw water is, in particular, water from the condensate of the exhaust gas of the steam turbine. The raw water can also be river water, seawater or wastewater, or originate from a further water source. Owing to the process of evaporation, it is possible even to use highly fouled wastewater. Depending on the amount of the raw water which arises from the condensate of the exhaust gas of the steam turbine, in this manner, still more water can be fed to the process.

In a further embodiment of the invention, the temperature of the raw water in the evaporator is from 60° C. to 100° C. Owing to this low temperature level, it is advantageously possible to heat the raw water only by means of the waste heat of the steam circuit, in particular the steam generator, or the exhaust gas of the steam turbine. This is advantageously highly energy-saving.

In a further embodiment of the invention, the heater is operated with the heat of the exhaust gas of a steam generator of the steam turbine process. The water treatment therefore advantageously succeeds virtually without additional electrical energy input. The required thermal energy is advantageously completely withdrawn from the steam circuit or the exhaust gas of the steam turbine process.

In a further embodiment of the invention, the evaporator is a falling-film evaporator or a trickle-flow evaporator. In the case of these evaporator embodiments, advantageously the boundary surface between the carrier gas, in particular air, and the raw water is particularly high in order to permit mass transport and heat transfer. Typically, the carrier gas is conducted from bottom to top, and the raw water from top to bottom.

FIG. 1 shows an arrangement 1 having a coupling of the steam turbine power plant to the thermal water treatment arrangement 5. By way of example, in FIG. 1 only one turbine stage 2 is shown. The steam generator 4 generates fresh steam 7 from boiler feed water 14 using a heat supply 12, typically an external heat source. The fresh steam 7 is then passed into the turbine 2 for electricity generation. The exhaust gas 6 which is formed in the steam generation 4 is passed to a heater 15 which heats the raw water 10 of the thermal water treatment arrangement 5. The steam 8 leaves the turbine 2 and is then condensed in a first condenser 3 to form condensate 9. A part of this condensate 9 is passed as raw water 10 to the thermal water treatment 5. It is likewise possible to conduct all of the condensate 9 into the thermal water treatment 5. For the thermal water treatment 5, in addition fresh raw water 11 can be added from another external source. This can be, for example, seawater or river water. After the water treatment 5, raw water 19 that is concentrated with contaminants leaves the thermal water treatment arrangement 5. In addition, cleaned up water 22 leaves the thermal water treatment arrangement 5. The boiler feed water 14 is then in turn fed to the steam generator 4. Depending on the degree of contamination of the steam 8 or the condensate 9, a cleaned up fraction of boiler feed water 14 can be mixed with a fraction that is not cleaned up of condensate 9 to form boiler feed water 14.

In the event that the heat of the exhaust gas 6 is insufficient after the steam generation in the steam generator 4, in addition, at various points of the steam circuit in the case of a plurality of turbine stages, also between the stages, heat can be taken off in order to heat the heater 15.

FIG. 2 shows the thermal water treatment arrangement 5 in detail. The core part of the thermal water treatment arrangement 5 is the evaporator. In this example, in particular a trickle-flow evaporator 16 is used. In this case the raw water 10 that is to be cleaned up flows from top to bottom through a structured evaporator packing. The air 13 as carrier gas is conducted from bottom to top through the trickle-flow evaporator 16. The temperatures in the trickle-flow evaporator 16 are in a range between 60° C. and 100° C. The trickle-flow evaporator 16 operates by means of a convectively supported evaporation of water. The pure water evaporates into the air 13 that is conducted in counter flow and the pure water can then be condensed back in a second condenser 17 and conducted as clean water 22 back into the steam generator 4. The second condenser 17 is cooled with raw water 10. The already-heated raw water 18 is then conducted through the heater 15 in order to bring the raw water to the temperature that is required in the trickle-flow evaporator 16. The raw water 18 is then trickled over a suitable evaporator material. Materials that are used are in particular structured packings made of plastic, metal or cellulose having a specific surface area from 100 m²/m³ to 300 m²/m³.

The trickle-flow evaporator 16 is operated in counter flow. That means that the temperature of the downwardly flowing raw water 18 decreases from the top to the foot of the trickle-flow evaporator 16, because energy is withdrawn from the water by evaporation and air heating. The temperature of the countercurrent air, in contrast, increases from the foot to the top of the trickle-flow evaporator 16. At a separation stage, that is to say at a height in the trickle-flow evaporator 16, the temperature of the air always stays lower than the temperature of the raw water. The heat transfer thereby proceeds from the falling water to the ascending air, and corresponding to the ascending temperature, the air can take up more steam in the upper region of the trickle-flow evaporator 16. The raw water 19 that is concentrated with contaminants is charged in part into a tank 20 for storage, in part it is transported out of the system. Depending on the demand quantity of the boiler feed water 14 and on the quality of the concentrated raw water 19, the tank 20 is filled with fresh raw water 11. The fresh raw water 11 can on one hand be the condensed water from the turbine 2, but on the other hand, can also be water from other water sources such as, for example, river water, seawater or wastewater of a sewage treatment plant. The advantage of the evaporation method used is that the treatment even of highly fouled wastewaters is possible.

The boiler feed water 14 is typically conditioned upstream of the steam generation for operation of the steam turbine in such a manner that the corrosion tendency decreases. This takes place, for example, with the addition of volatile alkalizing agents, in particular ammonia. Usual ammonia concentrations are, depending on the procedure, in a range from 0.5 mg/l to 1 mg/l (with addition of phosphate) or >5 mg/l (without phosphate addition). Ammonia can, however, in excessive concentrations, in the presence of foreign ions such as phosphate, in turn lead to corrosion, in particular on account of the formation of ammonia salts, in the heating steam circuit. Therefore, depending on the procedure, it can be necessary to remove ammonia from the system in the thermal water treatment arrangement 5. Ammonia is a volatile component and, without a conditioning of the raw water would convert to the gas phase in the trickle-flow evaporator 16 and thus pollute the cleaned-up water. In order to prevent this, the pH of the raw water 18 is adjusted in such a manner that it is at least one pH unit below the pKa of ammonia of 9.2. In this pH range, the ammonia is present in water as ammonium ion. The ammonium ion is hydrolyzed and as a result less volatile. Therefore, in the trickle-flow evaporator 16, it does not transfer into the gas phase, but leaves the trickle-flow evaporator 16 with the concentrated raw water 19. Ammonia can then be added again to the boiler feed water 14 in the desired concentration.

In the event that ammonia is not to be removed 10 from the raw water, a pH can be selected that is at least one pH unit above the pKa of 9.2. Thus, ammonia can be conducted into the second condenser 17 together with the air 21 that is loaded with the purified water. Said water can be recirculated directly as conditioned boiler feed water 14 to the steam circuit of the turbine 2. In such a mode of operation, however, ammonia is enriched on account of its high vapor pressure in the condensate of the water treatment plant.

The necessity of removing the ammonia depends on several factors. Firstly, the type of the boiler feed water conditioning is critical. In the event that the ammonia concentration is to be restricted, it is necessary to heed whether, as shown in FIG. 1, a part of the condensate 9 downstream of the turbine 2 is conducted directly back into the steam generator 4. In the event that a part of the condensate 9 is conducted directly without treatment into the steam generator 4, a cleanup is also dependent on the ratio of said amount of condensate 9 to the amount of raw water 10 used. This condensate 9 that is not cleaned up contains ammonia in a defined concentration. Depending on said concentration, now in the thermal water treatment 5, the ammonia must be correspondingly decreased, in order to set the desired ammonia concentration in the boiler feed water 14.

In the event that ammonia is not to be completely removed from the raw water 10, but also is not to remain completely in the raw water 10, or is even to be concentrated, there is the possibility, by corresponding choice of a pH within the range (pKa−1)<pH<(pKa+1) to set the desired ammonia concentration. 

What is claimed is:
 1. A method for operating a steam turbine plant in combination with a thermal water treatment plant, the method comprising: condensing steam from the stream turbine plant to raw water in a first condenser, adding a carrier gas and at least one fraction of the raw water to an evaporator, wherein mass transfer and heat exchange between the raw water and the carrier gas occurs in the evaporator, conducting the raw water and the carrier gas in counter flow in the evaporator, wherein the carrier gas heats up in the evaporator and takes up pure water from the raw water and the raw water cools and the contaminants concentrate, collecting the raw water with the concentrated contaminants downstream of the evaporator in a tank, conducting the carrier gas loaded with pure water into a second condenser, condensing purified water from the carrier gas in the second condenser, wherein the second condenser is cooled by the raw water from the tank, conducting the purified water into a steam circuit of the steam turbine plant, conducting the preheated raw water from the second condenser to a first heater, wherein heat from the steam turbine plant or the steam circuit transfers to the preheated raw water, and conducting the preheated raw water from the heater into the evaporator.
 2. The method of claim 1, wherein the raw water comprises ammonia, and the pH of the raw water is adjusted to be acidic such that the ammonia in the evaporator remains in the raw water.
 3. The method of claim 1, wherein the raw water comprises ammonia, and the pH of the raw water is adjusted to the basic such that the ammonia transfers into the carrier gas.
 4. The method of claim 1, comprising adding fresh raw water to the tank.
 5. The method of claim 4, wherein the fresh raw water is condensate water from the exhaust gas of the steam turbine, river water, seawater, or wastewater.
 6. The method of claim 1, wherein the temperature of the raw water in the evaporator is in the range of 60° C. to 100° C.
 7. The method of claim 1, comprising operating the heater with the heat of the exhaust gas of a steam generator of the steam circuit.
 8. The method of claim 1, comprising using air as the carrier gas.
 9. A system for operating a steam turbine plant in combination with a thermal water treatment plant, the system comprising: a first condenser configured to condense steam from the steam turbine plant to raw water, an evaporator configured to operate with raw water and a carrier gas, wherein mass transport and heat exchange occurs in the evaporator, a tank configured to collect the raw water that is concentrated with contaminants, a second condenser configured to condense the pure water from the carrier gas downstream of the evaporator, and at least one steam turbine configured to operate with at least a fraction of the purified water.
 10. The system of claim 9, wherein the evaporator is a falling-film evaporator or a trickle-flow evaporator. 